Total temperature probe and total temperature determination method

ABSTRACT

The invention relates to a total temperature probe for an aircraft and to a method of determining temperature by means of such a probe. The total temperature measurement probe comprises a base, an external face of which is intended to be mounted so as to be substantially coplanar with a skin of the aircraft, and a mast that projects from the base and supports an active part of the probe. The probe furthermore includes several temperature sensors placed on, the external face of the base and distributed around the mast. The method consists in determining the total temperature of the air surrounding the probe on the basis of the temperature measurement carried out in the active part ( 4 ) of the probe and on the basis of the maximum difference that exists between the measurements made by the temperature sensors.

The invention relates to a total temperature probe and to a method ofdetermining temperature by means of such a probe.

A total temperature probe measures the total temperature of the air flowin which it is placed. When the speed of the air flow is high enough, atemperature measurement element placed in the probe takes thetemperature of the air thanks to the convection effect. When the speedof the flow is low or zero, the measurement is affected by variousfactors, among which is the heating needed for deicing and the solarradiation, which factors have the effect of raising the temperature ofthe probe to a value above that of the surrounding air.

It is possible to correct the measurement error due to the influence ofthe heating by means of calibrations and by modeling, taking intoaccount several parameters such as the heating power dissipated in theprobe and the speed of the flow, which also has to be measured, or bythe probe itself in the case of a multifunction probe, such as thatdisclosed in French patent application FR 2 802 647 filed on Dec. 17,1999.

Such modeling does not take into account the rise in temperature of theprobe that is caused by solar radiation. More precisely, when anaircraft on which the probe is mounted is in flight phase, the speed ofthe flow of air surrounding the probe is sufficient for the effect ofsolar radiation to be negligible and the modeling described above issufficient. However, when the aircraft is placed on the ground, theeffect of solar radiation becomes important and the temperaturemeasurement is impaired.

A first solution for avoiding the effect of solar radiation consists infitting the probe in a region protected from sunshine, for example underthe fuselage. As a result, the installation constraints may becontradictory with in-flight use of the probe. The regions protectedfrom sunshine are, in general, aerodynamically disturbed by the landinggear.

Another solution for eliminating the effect of heating and of solarradiation when the speed of the flow is low or zero consists in causingforced convection around the measurement element of the probe. Thisrequires a pressure source capable of a certain flow rate, which causes,for example by suction, movement of air around the measurement elementof the probe.

The latter solution is highly prejudicial from the standpoint of fittingthe probe on the aircraft. It requires the installation of specific airsuction ducts in the vicinity of each temperature probe and the fittingof a pressure generator. This solution is therefore very expensive.

The object of the invention is to alleviate the abovementioned problemsby allowing the temperature of the probe to rise due to solar radiationand by correcting the measurement error that it induces.

For this purpose, the object of the invention is to propose means forcorrecting the measurement error due to the effect of solar radiation onthe temperature measurement carried out by the probe.

More precisely, the subject of the invention is a total temperaturemeasurement probe for an aircraft, comprising a base, an external faceof which is intended to be mounted so as to be substantially coplanarwith a skin of the aircraft, and a mast that projects from the base andsupports an active part of the probe, characterized in that itfurthermore includes several temperature sensors placed on the externalface of the base and distributed around the mast.

The subject of the invention is also a method of determining temperatureby means of the total temperature probe defined above and characterizedin that the total temperature of the air surrounding the probe isdetermined on the basis of the temperature measurement carried out inthe active part of the probe and on the basis of the maximum differencethat exists between the measurements made by the temperature sensors.

Of course, the invention is not limited to a probe having onlytemperature sensors. The invention may especially be employed inmultifunction probes having, in addition to temperature sensors, othertypes of sensors such as pressure sensors.

The invention will be more clearly understood and other advantages willbecome apparent on reading the detailed description of one embodiment ofthe invention, this description being illustrated by the appendeddrawing in which:

FIG. 1 shows, in perspective, a total temperature measurement probe.

The probe shown in FIG. 1 comprises a base 1, an external face 2 ofwhich is intended to be mounted so as to be substantially coplanar witha skin of an aircraft on which the probe is mounted. The probe alsoincludes a mast 3 that projects from the base 1. The mast 3 supports anactive part 4 of the probe. The active part 4 includes an air inlet 5via which a stream of air, the total temperature of which it is desiredto determine, penetrates. Inside the active part 4, a temperature sensorperforms the total temperature measurement by the probe. For furtherdetails relating to the construction of the active part 4 of the probe,the reader may refer to the French patent application published underthe number FR 2 802 647.

According to the invention, the probe has several temperature sensors 6to 9 placed on the external face 2 of the base 1. The sensors 6 to 9 aredistributed around the mast 3. These temperature sensors 6 to 9 eachcomprise, for example, a thermocouple whose hot junction is locatedlevel with the external face 2 of the base 1. In FIG. 1, four sensors 6to 9 have been shown. Of course, the invention is not limited to foursensors. The number of temperature sensors and their positions may bedetermined, during design of the probe, according to its shape.

Advantageously, the temperature sensors 6 to 9 are thermally insulatedfrom the external face 2 of the base 1. Thus, they will be lessdisturbed by any conduction tending to make the temperature of the base1 uniform.

Advantageously, the probe includes at least three temperature sensors.Thus, when the probe is subjected to solar radiation, at least one ofthe sensors is in the shadow of the mast 3 or of the active part 4.

To determine the total temperature of the air surrounding the aircraft,by means of the probe described above, the maximum difference thatexists between the various measurements made by the temperature sensors6 to 9, one of the sensors 6 to 9 being in the shade, is determined. Themaximum difference is representative of the solar radiation reaching theprobe. Next, the temperature measurement performed by means of theactive part 4 of the probe can be corrected using this maximumdifference.

The correction of the temperature measurement made by means of theactive part 4 can be calibrated, for example by varying the radiationreaching the probe and by noting, for a given total temperature of theair surrounding the probe, the values measured by the active part 4 ofthe probe and by the sensors 6 to 9, and doing so for various values ofthe radiation. This calibration makes it possible to determine thedifference between the measurement made by the active part 4 of theprobe and the actual total temperature of the air surrounding the probeon the basis of the measurements made by the temperature sensors 6 to 9.This calibration may be carried out for several levels of radiationreaching the probe. Each level of radiation will give a maximumdifference between the measurements made by the temperature sensors anda difference between the measurement made by the active part 4 and theactual total temperature of the air surrounding the probe. The actualtotal temperature may be measured by the active part 4 in the absence ofany radiation.

During normal use of the probe, it will be possible to determine, fromthe maximum difference between the measurements made by the temperaturesensors 6 to 9, a correction to be applied to the measurement made bythe active part 4 of the probe, for example by interpolation betweenresults obtained for each level of radiation during the calibration.

Advantageously, the total temperature of the air surrounding the probeis determined as a function of the speed of the air surrounding theprobe. This is because the effect of solar radiation decreases when thespeed of the air surrounding the probe increases. As previously, thecorrection to be made to the temperature measurement carried out by theactive part 4 of the probe can be calibrated. This calibration may becarried out in a wind tunnel, by varying the speed of an airflowsurrounding the probe while illuminating it with a given level ofradiation.

1. A total temperature measurement probe for an aircraft, comprising: abase, an external face of which is intended to be mounted so as to besubstantially coplanar with a skin of the aircraft, and a mast thatprojects from the base and supports an active part of the probe, whereinit furthermore includes several temperature sensors placed on theexternal face of the base and distributed around the mast.
 2. The probeas claimed in claim 1, wherein the temperature sensors are thermallyinsulated from the external face of the base.
 3. The probe as claimed inclaim 1, wherein it includes at least three temperature sensors.
 4. Amethod of determining temperature by means of a total temperature probeas claimed in claim 1, wherein the total temperature of the airsurrounding the probe is determined on the basis of the temperaturemeasurement carried out in the active part of the probe and on the basisof the maximum difference that exists between the measurements made bythe temperature sensors.
 5. The method as claimed in claim 4, whereinthe total temperature of the air surrounding the probe is determined asa function of the speed of the air surrounding the probe.
 6. The probeas claimed in claim 2, wherein it includes at least three temperaturesensors.